Laundry detergents comprising anionic detersive surfactants for cleaning fabrics have been known for many years. Historically, cleaning laundry was defined primarily as a process that involved removal of stains. Consistent with this historical approach to cleaning, laundry detergent designers focused on formulating with large amounts of anionic surfactants to ensure maximum surface activity of the surfactants to achieve the most removal of soil. However, to rinse off such laundry detergents with high surfactant levels require a large amount of water and multiple rinse cycles, which poses a challenge for consumers living in areas where water is scarce. Further, as the modern society becomes more and more conscious of the environmental impact of synthetic surfactants and cleaning additives, there is a continuing need for laundry detergents and cleaning compositions with lower levels of surfactants while still maintaining the cleaning benefits thereof.
Consumers typically view copious suds in the wash as the primary and most desirable signal of cleaning. High suds are especially desirable during hand washing of fabrics, since the consumer can directly feel and touch the suds generated during the wash cycle and will intuitively correlates the high suds volume with the achievement of sufficient fabric cleaning. As fabrics, consumer habits and chemistries evolve, consumers are recognizing that cleaning of soils off fabrics is no longer the only or even biggest challenge they meet. As consumers become more sophisticated, they are recognizing that surfactants that generate copious suds in the wash also do not rinse well and tend to leave chemical residues on fabrics. Therefore, if suds are still present during the rinse, then the consumers immediately infer from it that there may still be surfactant residue on the fabrics and that the fabrics are not yet “clean”. As a result, the consumers feel the need to rinse the fabrics multiple times in order to make sure that the surfactants are removed as thoroughly as other soils. Hence, while a large volume of suds is desirable during the wash cycle of fabric cleaning, it is paradoxically undesirable during the rinse cycle.
Linear alkyl benzene sulphonate (LAS) is one of the most commonly used anionic surfactants in laundry detergents. Although sufficient cleaning can be achieved by using detergent compositions with relatively lower levels of LAS, e.g., 20 wt % or less, the volume of suds generated by such detergent compositions is significantly reduced. The reduced suds volume during the wash cycle will inevitably perceived by the consumers as ineffective cleaning, which is in turn correlated with inferior quality of the laundry detergents used. In order to avoid such negative consumer perception, one or more co-surfactants can be added into the detergent compositions to boost suds volume during the wash cycle for detergent compositions containing relatively lower levels of LAS surfactant. Alkylethoxy sulfates (AES) are particularly effective in boosting wash suds volume when used in combination with LAS. However, AES tends to leave a significant amount of suds after the wash cycle, and laundry detergent compositions containing AES require multiple rinses for complete elimination of the suds.
There is therefore a continuing need for an improved laundry detergent composition, particularly a stable liquid laundry detergent composition, which contains relatively lower levels of LAS with little or no AES, but which is tuned to provide an optimal sudsing profile, i.e., a sufficiently high level of suds during the wash (signaling effective cleaning) and subsequently a reduced suds volume during the rinse, so that consumers perceive the surfactants as capable of being easily rinsed away, preferably in a single rinse cycle.